#include <iostream>
#include <vector>
using namespace std;
struct TreeNode
{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() : val(0), left(nullptr), right(nullptr){}  TreeNode(int x) : val(x), left(nullptr), right(nullptr){}  TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right){}                                                                                      
};
    class Solution
{
public:
    TreeNode* build(vector<int>& preorder,vector<int>& inorder,int& prei,int inbegin,int inend)
    {
        if(inbegin > inend)
        {
            return nullptr;
        }
        TreeNode *root = new TreeNode(preorder[prei]);
        int rooti = inbegin;
        while(rooti <= inend)
        {
            if(inorder[rooti] == preorder[prei])
            {
                break;
            }
            else
            {
                rooti++;
            }
        }
        prei++;
        root->left = build(preorder, inorder, prei, inbegin, rooti - 1);
        root->right = build(preorder, inorder, prei, rooti + 1, inend);
        return root;
    }
    TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder)
    {
        
        int i = 0;
        return build(preorder, inorder, i, 0,inorder.size() - 1);
    }
};